Can you export jpeg images from Publisher? If so you could make up a document in publisher. Add you logo etc. , then export them, as jpegs. Don't make the page too big .
You may have to experiment.
Along the same lines as John's suggestion, if you wanted to do this in Word it's relatively easy.
(I'm not particularly familiar with Publisher so can't help you with that)
Insert your jpeg into a new Word document.
Open a text box over the jpeg and choose your font size and colour - then arrange the text as you want to see it over the top of your image.
Group the jpeg and the text box together, then save the image as a new jpeg.
You could even save a copy of the text box to a blank document to reuse on subsequent photos.
It's not a particularly elegant solution and no real substitute for proper editing software, but you will get something resembling the result that you want.
Longer term, editing software is the way forward and there are some free packages out there as suggested above.
Just to pick up on another point that was touched on above, watermarking is by no means a necessity for showing your images on Flikr.
You automatically have legal copyright to them and as long as they're at a small size, they're not much use for anyone to do anything else with.
IMO unless the watermark is very discreet it really does detract from the image you want to show . . . and if it
is very discreet anyone intent on using your images illegally would be able to clone it out.
